This invention relates to infrared communications and, more particularly, to fast infrared transceivers having low standby power consumption.
Electronic devices such as portable computers, electronic organizers, personal digital assistants, and cellular telephones, use infrared communications. The devices typically adhere to one of the Infrared Data Association (IrDA) infrared communication standards. The IrDA standards are based on the OSI seven-layer model. Presently, there are two generations of standards in the IrDA family: the 1.0 generation and the 1.1 generation. IrDA 1.0 sets a maximum data rate (aka signaling rate) of 115,000 bits per second (115 kbps) over a communications link. IrDA 1.1 sets a maximum data rate of 4,000,000 bits per second (4 Mbps) over the communications link. When using current technology, data rates over 200 kbps can be considered high-speed.
An infrared communications link usually incorporates a combination infrared transmitter and receiver, known as a transceiver. The transceiver transmits a modulated infrared signal and receives modulated infrared signals. An IR transceiver always operates in one of four modes: shutdown, standby, receive, or transmit.
In shutdown mode, the transceiver consumes almost no power. It is not capable of receiving or transmitting while in shutdown mode. Thus the transceiver cannot detect when another device attempts to establish an infrared communication link. The user generally must manually xe2x80x9cwakeupxe2x80x9d the transceiver from shutdown mode.
In standby mode, the transceiver consumes more power than when in shutdown mode but less than when in transmit or receive mode. The transceiver may detect infrared transmissions when in standby mode but may not receive or transmit. This ability to detect infrared transmissions is an important functional difference between standby mode and shutdown mode.
The xe2x80x9cactivexe2x80x9d modes of a transceiver are receive mode and transmit mode. During reception, the transceiver operates in receive mode. During transmission it operates in transmit mode. Active modes consume more power than standby or shutdown modes.
High power consumption in transceivers for fast infrared links (for example the 4 Mbps IrDA 1.1 implementation) is at least partially due to the power required by the receiver stage. High-speed receivers generally consume more power than low-speed receivers do, even when operated in standby or shutdown mode. In active mode, a 4 Mbps capable receiver consumes more power than the slower 115 kbps receiver, regardless of the speed at which the 4 Mbps receiver is actually receiving data. In other words, even if both are operated at 115 kbps, a 4 Mbps receiver consumes much more power than a 115 kbps receiver.
Additional general background, which helps to show the knowledge of those skilled in the art regarding the system context, and of variations and options for implementations, may be found in the following from the IrDA 1.0 and 1.1 families of standards: IrDA Serial Infrared Physical Layer Link Specification; IrDA Serial Infrared Link Access Protocol (IrLAP); IrDA Serial Infrared Link Management Protocol (IrLMP); IrDA Tiny TP; IrDA Command and Control Ir Standard (formerly known as IrBus); IrDA Infrared Communications Protocol 1.0; IrDA Infrared Tiny Transport Protocol 1.1; IrDA Infrared LAN Access Extensions for Link Management Protocol 1.0; IrDA Object Exchange Protocol 1.2; IrDA Minimal IrDA Protocol Implementation; IrDA Plug and Play Extensions; IrDA Infrared Mobile Communications; and IrDA Infrared Transfer Picture Specifications; all of which are hereby incorporated by reference. IrDA standards and protocols are available over the internet from the Infrared Data Association at www.irda.org.
Disclosed is a circuit and method to dramatically reduce power consumption of fast infrared links without putting the link in shutdown mode. A low speed, low power-consumption infrared receiver preamplifier is used in conjunction with a higher speed, higher power-consumption infrared receiver preamplifier. While waiting for an IR link to be initiated, the low-power preamplifier operates in standby mode and the high-power preamplifier is shutdown to reduce power consumption. When the low power receiver preamplifier detects an infrared transmission, the high power receiver preamplifier can be activated if high-speed communication is needed. Unlike power-saving schemes that put the link in shutdown mode, infrared communications are continuously available by use of the disclosed innovations. Thus a user does not have to manually xe2x80x9cwake upxe2x80x9d the infrared receiver to receive a message.
At the system level in a disclosed embodiment, a communications link between two devices using IrDA standards is initiated with a simple 9.6 kbps modulation. After the communications link is initiated at 9.6 kbps, a communication speed for further communication over the link is negotiated between the two devices. Bit rate negotiations and link control are discussed in IrDA Serial Infrared Link Access Protocol.
A 115 kbps transceiver can receive and transmit the necessary 9.6 kbps modulation required to negotiate a communications link. Therefore, every time two IrDA systems (including the faster 4 Mbps IrDA 1.1 devices) establish a connection, they could initiate the connection with a low power 115 kbps receiver rather than a higher power consumption 4 Mbps receiver.
Disclosed is a transceiver with a single receiver having two preamplifiers. A low power consumption, low-speed infrared receiver preamplifier stage is used in combination with a higher power consumption, higher speed infrared receiver preamplifier stage. The higher speed preamplifier can be put in shutdown mode to conserve power while the lower power consumption preamplifier remains in standby. This allows a high-speed transceiver to remain in continuous standby while awaiting an infrared message, yet limit power consumption while waiting. In the presently preferred embodiment, a 115 kbps preamplifer is used in combination with a 4 Mbps preamplifier. In an alternate embodiment, dual receivers could be used instead of dual preamplifiers in one receiver. In other words the transceiver could have two receivers, perhaps one that operates at 115 kbps and one that operates at 4 Mbps. In another embodiment, the receiver(s) and transmitter could be physically separate, not together in a transceiver.
While waiting for a communication link to be initiated, the low power preamplifier stage is in standby and the fast preamplifier is in shutdown. After a high-speed connection is established, an IrDA-compliant controller switches the transceiver from the 115 kbps preamplifier stage to the 4 Mbps preamplifier stage. Compared to prior art 4 Mbps infrared transceivers, the innovative infrared transceiver consumes very little power when in standby mode because the fast preamplifier (which consumes the more power than the slower preamplifier) is in shutdown mode when it is not needed for communication.
The method and circuit allow a continuous infrared standby because power consumption is dramatically reduced. Low power consumption preamplifiers generally are considered to be those that have a standby current of less than 3 mA. For example, standby current in the presently preferred embodiment is reduced from over 3 mA to under 100 xcexcA at a supply voltage of 2.7V. Thus continuous infrared standby is now a viable option for battery powered devices that incorporate the disclosed innovations for fast infrared communications.